The present invention relates to a structure of an ATM switching system used in a network performing communication in an asynchronous transfer mode (hereinafter referred to as an ATM).
A conventional ATM switching system (referred to also as an ATM exchange or an ATM switch) had generally a structure in which one call processing device (processor) is provided in an ATM switching system, and call processing such as protocol processing of a signaling message which is call processing requirement, routing selection, switch control and administration of calls is performed based on the control of the call processing device. Furthermore, when a large scale switching system is constructed, an ATM switching system of what is called a multiprocessor type in which call processing devices are provided in a plurality of units in such a way that the structure of the system is divided and increased in accordance with the function and the load of call processing or a plurality of systems are added so as to cope with the increase of call processing is constructed in general. For example, an ATM switching system such as disclosed in JP-A-7-235928 may be given. According to this ATM switching system, an ATM switching system provided with a plurality of call processors and having large processing capacity by respective processors performing call processing of lines allocated out of a plurality of lines accommodated in the ATM switching system and processed with switching, thereby to disperse the load of call processing, is realized.
However, the allocation of lines to the call processors when the system is used practically is fixed. Therefore, in case a fault is generated in one call processor, the lines allocated to the call processor become unusable. Further, dynamic load sharing by allocating lines to the call processor with the fluctuation of the load required for call processing during operation is not performed. Furthermore, it is structured so that the allocation of line interfaces to the call processing devices can be altered by means of software by transmitting and receiving a control message between a call processor and respective line interfaces through a virtual channel of an ATM switch which can be altered by software. However, restructure from cells into control messages becomes necessary in the line interface portion, and the structure of the line interfaces becomes complicated.
As described above, the development of an ATM communication network, in particular the development of an ATM switching system, has been commenced from providing a system of a larger scale or aiming at high processing capacity. However, the scope of introduction of ATM communication has been expanded rapidly in recent years and is going to be applied to small scale multipliers (MUX) and LANs used at locations near terminals of subscribers. Moreover, since the data to be processed by those communication apparatus are various, variety of call processing configurations have become required. Namely, it is desirable to provide not only an ATM switching system aiming at a large scale, but also an ATM switching system having a structure which is applicable from small scale to large scale ATM switching systems. Moreover it is described to have a structure capable of diverse call processing so that various communication services can be offered to various users.